Anticrack Nucleation as Triggering Mechanism for Snow Slab Avalanches

Heierli, Joachim; Gumbsch, Peter; Zaiser, Michael

doi:10.1126/science.1153948

Cited by 132 publications

(209 citation statements)

References 11 publications

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“…As weak layers benefit from lateral homogeneity to propagate fractures (Heierli et al, 2008), in the future the continuity or discontinuity of these point gradients could provide additional information for the analysis of weak layer metamorphism and stability.…”

Section: Discussionmentioning

confidence: 99%

“…Further, natural weak layers within the snowpack are often only a few millimetres thick (Heierli et al, 2008), suggesting that temperature gradients across small distances may be of interest. And temperature gradients -measured across distances of more than 1 cm -below the kinetic threshold have nevertheless yielded faceting and a coarse granular structure in the field (Jamieson, 2006;Smith et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Use of a thermal imager for snow pit temperatures

2012

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Abstract. Weak snow of interest to avalanche forecasting often forms and changes as thin layers. Thermometers, the current field technology for measuring the temperature gradients across such layers -and for thus estimating the expected vapour flux and future type of crystal metamorphism -are difficult to use at distances shorter than 1 cm. In contrast, a thermal imager can provide thousands of simultaneous temperature measurements across small distances with better accuracy. However, a thermal imager only senses the exposed surface, complicating its methods for access and accuracy of buried temperatures. This paper presents methods for exposing buried layers on pit walls and using a thermal imager to measure temperatures on these walls, correct for lens effects with snow, adjust temperature gradients, adjust time exposed, and calculate temperature gradients over millimetre distances. We find lens error on temperature gradients to be on the order of 0.03 • C between image centre and corners. We find temperature gradient change over time to usually decrease -as expected with atmospheric equalization as a strong effect. Case studies including thermal images and visual macro photographs of crystals, collected during the 2010-2011 winter, demonstrate large temperature differences over millimetre-scale distances that are consistent with observed kinetic metamorphism. Further study is needed to use absolute temperatures independently of supporting gradient data.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Use of a thermal imager for snow pit temperatures

2012

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“…The formulation of McClung [2009a] is a quasi-brittle model based on rate dependent modulus, finite FPZ, pressure sensitivity and strain-softening behavior which are known properties of alpine snow. Detailed evaluations of the models of Heierli et al [2008] andMcClung [2009a] are beyond the scope of this paper since the uncertainties contained in the models are greater than the correction term to 2L implied by the data in section 4.…”

Section: Appendix A: Some Features Of the Propagation Saw Tests In Rementioning

confidence: 99%

“…[54] Two models have been developed in relation to explanation of the propagation saw tests, namely, those of Heierli et al [2008] andMcClung [2009a]. I regard both as simplified models of the complex process in the saw tests.…”

Section: Appendix A: Some Features Of the Propagation Saw Tests In Rementioning

confidence: 99%

“…I regard both as simplified models of the complex process in the saw tests. The model of Heierli et al [2008] is based on linear (rate independent) elasticity with infinitesimal fracture process zone. The formulation of McClung [2009a] is a quasi-brittle model based on rate dependent modulus, finite FPZ, pressure sensitivity and strain-softening behavior which are known properties of alpine snow.…”

Section: Appendix A: Some Features Of the Propagation Saw Tests In Rementioning

confidence: 99%

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The critical size of macroscopic imperfections in dry snow slab avalanche initiation

McClung

2011

J. Geophys. Res.

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[1] Dry snow slab avalanches initiate after mode II fracture propagation within a thin, weak layer under a planar slab. Dry alpine snow in which avalanches form is a porous material, typically with volume fraction filled by solids of between 10% and 50%. If snow slab avalanches were caused by small scale flaws, there would be continuous avalanches and alpine snow would not survive on steep slopes. Instead, snow slab avalanches initiate from macroscopic imperfections or weak zones within the weak layer. These are called "sweet spots" by practitioners and deficit zones in the pioneering work by Conway and Abrahamson in the 1980s. In this paper, the results of 750 in situ shear fracture tests from 68 slab-weak layer combinations are summarized in relation to the critical sweet spot length and weak layer crystal form. The results show that the critical sweet spot lengths follow a gamma probability density function with a range from 0.14 to 1.3 m and most probable value 0.5 m. The results also imply that critical sweet spot length depends on weak layer grain type with significantly larger values for persistent forms (surface hoar and facets) than for nonpersistent forms (decomposing and fragmented grains).

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A new mixed‐mode failure criterion for weak snowpack layers

Reiweger¹,

Gaume²,

Schweizer³

2015

Geophysical Research Letters

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The failure of a weak snow layer is the first in a series of processes involved in dry‐snow slab avalanche release. The nature of the initial failure within the weak layer is not yet fully understood but widely debated. The knowledge of the failure criterion is essential for developing avalanche release models and hence for avalanche hazard assessment. Yet different release models assume contradictory criteria as input parameters. We analyzed loading experiments on snow failure performed in a cold laboratory with samples containing a persistent weak snow layer of either faceted crystal, depth hoar, or buried surface hoar. The failure behavior of these layers can be described well with a modified Mohr‐Coulomb model accounting for the possible compressive failure of snow. We consequently propose a new mixed‐mode shear‐compression failure criterion that can be used in avalanche release models.

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Anticrack Nucleation as Triggering Mechanism for Snow Slab Avalanches

Cited by 132 publications

References 11 publications

Use of a thermal imager for snow pit temperatures

Use of a thermal imager for snow pit temperatures

The critical size of macroscopic imperfections in dry snow slab avalanche initiation

A new mixed‐mode failure criterion for weak snowpack layers

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